The present invention relates to a drive system for treadmills and more particularly to variable pitch belt drive transmissions to control the speed of the walking belt.
A treadmill is a motorized device that is used for exercise. By adjusting the speed of the walking belt, exercise can be performed at any desired level.
In one type of treadmill currently in use, the walking belt is driven by a synchronous AC drive motor which runs at a constant speed. To adjust the speed of the walking belt, the motor is connected to the walking belt through a variable transmission.
A typical variable transmission in use for such an application consists of two sets of adjustable sheave pulleys. The input pulley is connected to the shaft of the drive motor while the output pulley is connected to the walking belt. A main drive V-belt connects the two pulleys together.
The input pulley sheaves are conically shaped and the distance between the sheaves, which is adjusted by a speed adjust motor, determines the effective diameter of the pulley. The output pulley sheaves are similarly conically shaped and are forced together by internal springs. The main drive V-belt, which is of fixed length, adjusts the separation of the output pulley sheaves determined by how much of the belt is required by the input pulley (i.e., its effective diameter).
To decrease the speed of the walking belt, the input pulley sheaves are moved further apart by the speed adjust motor allowing the springs in the output pulley to drive the sheaves closer together, the effective diameter of the input pulley going down and the effective diameter of the output pulley increasing, thereby changing the input to output drive ratio of the transmission resulting in a slow down of the walking belt.
In order to adjust the input to output drive ratio of the transmission, the system must be moving to allow the main drive belt to be properly tensioned between the input and output pulleys. Attempting to adjust the transmission without the system moving, would cause either binding of the main drive belt between the input pulley sheaves when the input pulley sheaves are forced together or the total disengagement of the main drive belt from the input pulley when the sheaves are adjusted apart.
The user of the treadmill is instructed to bring the walking belt down to its slowest speed before turning the apparatus off so that the walking belt will start up at the slowest speed when the next user starts to use the machine. If the current user forgets to slow the walking belt down first, which is not an uncommon occurrence, then for the reasons noted above, it is not possible to get the machine at the slowest speed prior to its next use. Even when the machine is started at the slowest speed, the next user could incur a jolt or jerk when he or she starts the machine while standing on the walking belt with some injury possible if the transmission is left at high speed.
Thus, utilizing the speed reset motor to adjust the separation of the input pulley sheaves after the treadmill has been shut down will not cure the problem.
A number of United States patents show treadmill drive and belt drive transmission systems utilizing sheave separation to vary the output drive speed. They include U.S. Pat. Nos. 3,731,549, 4,088,036, 4,174,641, and 4,541,821. None of these patents shows a treadmill drive system utilizing adjustable input and output sheave separation for the control of the walking belt incorporating the principles of this invention.